The present invention relates to an optical information recording method for recording information by forming marks on a recording medium by irradiating a light, and a device thereof.
Various kinds of optical recording media for recording by forming optically identifiable marks by heat generated by irradiating a light (light beam) on a recording medium are discussed. One of the optical recording media is a phase-change type medium for recording by utilizing the thermal phase change between the crystalline and the amorphous. A recording film of a phase-change type medium is crystalline in a stationary state, but a region irradiated with a light changes from the crystalline to the amorphous by cooling after heating and melting. According to the principle, information can be recorded by forming an amorphous portion as a mark. As a recording method of such a phase-change type medium effective in improving the recording density, a PWM (pulse width modulation) where the positions of the starting end and the finishing end of a mark correspond with the information to be recorded can be presented.
In general, when the PWM method is applied to a phase-change type optical disk, a multi-pulse recording is conducted so as to reduce the heat accumulation caused by the light irradiation. The multi-pulse recording is a method where a plurally of divided light pulses but not a single light pulse (light pulse beam) is used as the irradiating light for forming a long mark. An example of such a multi-pulse recording is shown in FIG. 1. FIG. 1 is an example of recording information with an 8/16 modulation code with a mark length of a discrete value from 3T to 14T with respect to a recording window with T.
As shown in FIG. 1, a short mark of 3T, which is the shortest, is recorded with a single pulse of 1.5T. However, a long mark of 4T or more is recorded with a head pulse of 1.5T and sets of an erasing power period of 0.5T and a recording power period of 0.5T repeatedly for the length longer than 3T. That is, in the case of a long mark over 4T, subsequent pulses of 0.5T is added to a head pulse of 1.5T. For example, as shown in the right side of FIG. 1, in recording a mark of 6T, a set of an erasing power period of 0.5T and a recording power period of 0.5T are provided three times after a pulse of 1.5T. These light pulses may be generated synchronously with a recording clock.
However, even such a multi-pulse recording involves a problem in that positions of the starting end and the finishing end of a mark actually formed change from a predetermined position, depending upon the length of the mark. That is, as is later explained in detail, if the light irradiation is started with the same timing in the formation of both a short mark and a long mark, the heating conditions of the both are the same until the end of the head pulse irradiation. In the case of forming a short mark, utilizing only the head pulse, the heated and melted domain of a medium is cooled down to become amorphous. On the other hand, in the case of forming a long mark, utilizing the multi-pulse recording, the starting end position of the mark is shifted in the direction such that the mark length is shortened. The cause of the shift is attributed to the accelerated re-crystallization in the vicinity of the amorphous region since the region heated and melted by the head pulse is heated by the subsequent pulses again.
In the case the light irradiation is finished with the same timing in the formation of both a short mark and a long mark, the temperature distributions thereof after finishing the light irradiation are not always the same due to the heat characteristics of the medium. The medium temperature immediately after heating by the subsequent pulses is lower than the medium temperature immediately after heating by the head pulse. Therefore, as a consequence of a smaller molten domain after finishing the light irradiation, the finishing end position of a long mark is also shifted in the direction such that the mark length is shortened.
Accordingly, the starting end position and the finishing end position of a long mark are shifted in the direction such that the mark length is shortened more than the starting end position and the finishing end position of a short mark. In order to avoid the shift of the starting end position and the finishing end position of a mark depending upon the length of the mark so as to form a mark accurately, a recording compensation is needed. As a method of the recording compensation, a method of forming a mark with the head and tail positions of the irradiated light pulse preliminarily moved according to the length of a mark to be formed is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 7-129959.
However, in the recording compensation method, a light pulse needs to be generated with change from a clock synchronization state, besides, the amount of the change needs to be adjusted depending upon the mark length. Since a complicated circuit such as a programmable delay line is necessary for that, it involves a problem of difficulty in achieving both accuracy and cost efficiency.
As mentioned above, in the conventional recording compensation method where a mark is formed with the head and tail positions of the irradiated light pulse preliminarily moved according to the length of a mark to be formed, since a light pulse needs to be generated with change from a clock synchronization state, besides, the amount of the change needs to be adjusted depending upon the mark length, it involves problems such as necessity of a complicated circuit and difficulty in achieving both accuracy and cost efficiency.
An object of the present invention is to provide an optical information recording method and apparatus including recording compensation capability for improving the accuracy of marks to be formed without a drastic cost increase, and a device thereof.